Neural blockade is associated with many complications. Among the most feared complication is accidental, unrecognized penetration of nervous system compartments containing cerebrospinal fluid (CSF). If puncture into the CSF is not noted immediately, or if it is incorrectly diagnosed, subsequent drug administration may lead to paralysis or death. Despite widespread use during surgery, childbirth and pain relief, current methods to detect CSF during and after neural blockade are unreliable, costly and time-consuming.
Patients undergoing epidural anesthesia and analgesia are at particular risk for needle puncture into the CSF. The epidural space is identified prior to blockade by loss of resistance to syringe injection of air, or of water solutions containing salt or sugar. Placement of the needle in the epidural space is followed by injection of drugs dissolved in sugar- or salt-containing water solutions in serial increments. If the epidural blockade is to be maintained for a long interval, a catheter may be threaded through the needle for both continuous and intermittent injection of drug-containing solutions. Because penetration of the dura and unintended entry into the CSF is possible at any step, the needle and catheter are routinely observed for passive drainage of CSF, and aspirated for fluid return before each manipulation and drug administration. If CSF is present (a situation referred to as a Wet Tap), repositioning of the needle or catheter may be required to avoid spinal rather than epidural blockade upon drug injection.
Although unambiguous identification of drained or aspirated CSF is essential for the safe conduct of epidural anesthesia, caregivers are often uncertain over the origin of fluid that may be present. CSF is clear and watery, thereby closely resembling injected sugar- or salt-containing solutions and drug mixtures. In the past, efforts to discriminate CSF from injected or accumulated fluids have relied on physical properties such as temperature, or in vitro precipitation with second compounds, or on measurement of the possible chemical constituents of the fluid in question, such as glucose, protein, or ion levels. However, because of sample admixture, variability in test precision and inconsistent test thresholds, these methods are rarely helpful and little used.
At present, measurement of beta-2 transferrin in a sample is the only laboratory test to reach clinical practice capable of unequivocal discrimination of CSF, but its use is hampered in many regards. Each sample must be provided in high volume requiring as much as 1-2 mL of sample/assay. Turn-around time for results to reach the caregiver takes up to 4 days. Because immunofixation electrophoresis is necessary to detect beta-2 transferrin, the assay is expensive ($230-300/sample), and carries multiple added costs for specimen handling, archiving, shipping and storage, Moreover, special technical skills and experienced technicians are required to assure test precision and reliability, mandating that beta-2 transferrin assays be performed by specialty laboratories.
Clearly there is a great need for a rapid, robust, cost effective and accurate method to unambiguously identify CSF in samples obtained at the bedside during and after neural blockade.